1. Field of the Invention
The present invention relates to an improvement in a surface inspection apparatus for detecting a state of a surface of an object to be inspected.
This application claims priority under 35 U.S.C. § 119 to Patent Application Serial No. 2004-165671 filed in Japan on Jun. 13, 2005, the contents of which are incorporated herein.
2. Description of the Related Art
Heretofore, there has been known a surface inspection apparatus configured to detect a position of a foreign substance or a flaw or the like existing on a surface of an object to be inspected in a height-direction of the inspecting object, so as to detect the position of the foreign substance or the flaw or the like existing on the surface of the inspecting object accurately even when there is a warpage in the inspecting object (for reference, see JP-A 11-153549).
As shown in FIG. 1 for example, such a surface inspection apparatus is provided with an irradiation optical unit 3 for irradiating irradiation light P1 emitted from an irradiation light source 1 onto a wafer 2 as the inspecting object, a light-receiving optical unit 5 having a light-sensitive element 4 for receiving scattered light P2 of the irradiation light P1 irradiated from the irradiation optical unit 3 that is scattered by the foreign substance or the flaw or the like existing on a surface S of the wafer 2 and converting the received scattered light P2 into photoelectric conversion signals, and a light-receiving optical unit 7 having a light-sensitive element 6 for receiving specular reflection light P3 of the irradiation light P1 irradiated from the irradiation optical unit 3 that is specular-reflected from the surface S of the wafer 2 and converting the received specular reflection light P3 into photoelectric conversion signals.
The wafer 2 is displaced relative to the irradiation optical unit 3 and the light-receiving optical units 5 and 7 by using a rotational driving mechanism 8 and a linear movement mechanism 9 which are as relative displacement means. The rotational driving mechanism 8 and the linear movement mechanism 9 have a driving motor, respectively.
As shown in FIG. 2, according to such a surface inspection apparatus, when representing a surface of the wafer 2 located on a reference height Z1 by a symbol S and representing a surface of the wafer 2 in which a height is deviated by ΔZ in a height-direction (Z-direction) relative to the reference height Z1 by a symbol S′, and assuming that the specular reflection light P3 from a detecting position (irradiated detecting position) y1 at the time when a foreign substance (flaw) 10 is located on the surface S enters a light-receiving reference position Q0 of the light-sensitive element 6, a light-receiving position of the light-sensitive element 6 to which specular reflection light P3′ from the surface S′ of the wafer 2 enters will be a position Q1 deviated relative to the light-receiving reference position Q0 by ΔS. Accordingly, since there is a certain relation between the amount of deviation ΔS and the amount of deviation ΔZ, an amount of deviation Δy of a plane-coordinate-position y2 at the time when the surface S is deviated from the reference height Z1 by the height ΔZ as shown by the symbol S′, relative to a plane-coordinate-position y1 in a radial direction as the irradiated detecting position of the foreign substance (flaw) 10 at the time when the surface S is at the position of the reference height Z1, is obtained by a following formula based on the amount of deviation ΔS and a reflection angle θ:Δy=ΔS/tan θor a formula:Δy=ΔZ/tan θ
Therefore, the plane-coordinate-position y2 at the time when the irradiated detecting position is deviated relative to the reference height Z1 by the ΔZ is obtained by a following formula:y2=y1−Δy 
That is to say, it is possible to detect the foreign substance (flaw) 10 existing on the wafer 2 accurately even when there is the warpage in the wafer 2, by correcting the plane-coordinate position in the y-direction.
However, as shown in FIG. 3, when the surface S of the wafer 2 as the inspecting object is coarse, there is a possibility that the specular reflection light P3 of the irradiation light P1 specular-reflected from the surface S is deflected and misaligned as shown by a symbol P5 relative to a direction P4 of the specular reflection light P3 to which the irradiation light P1 (i.e. specular reflection light P3) should be reflected if there is no irregularity R, due to a local gradient caused by the irregularity R of the surface S.
Consequently, the conventional surface inspection apparatus has a problem that it is indistinguishable whether or not the irradiated detecting position of the foreign substance (flaw) 10 on the wafer 2 is deviated from the reference height position Z1.